Depends what you mean by pop-ups? Almost any bait can be popped up. Pop-up boilies, bread and plastic corn are the main ones. However, other artificial baits, worms, maggots and expander pellets can easily be used with good effect. Basically there are 2 rigs mainly used. The first is a bait popped up just off bottom and critically balanced by some shot. Meaning just enough shot to sink the popped up bait between 1 and 6 inches off the bottom generally on a 1 ft long tail/hook length. Where you place the shot dictates the depth the pop-up is fished off the deck. The other rig often used is a zig rig. The zig rig is just a fixed rig, although can also be used running and has a length of line/link/hook length suspended by the pop-up bait X feet off the deck. The line/hook length can be anything from 6 inches long to as long as you want. As an example. An 8ft long tail/hook length fished 6 inches from the surface in an 8 ft 6 inch deep swim. Shorten the tail/hook length to 5ft 6 inches to fish the pop-up 3 ft from the surface in the same depth of water. Generally, feeding is only when fishing a pop-up close to the bottom with the critically balanced bait. Feed similar sinking items such as corn, sinking boilies or partical feeds like pellets and hemp, ect. With the zig rig. Its less about feeding and more about finding the depth the fish are sat at. However, feeding a few sinking boilies, pellets, corn to make some noise to attract fish in to your swim can work. Finally, mainly in summer. Adding a cage feeder instead of a bomb can then allow feed to be added to the swim while fishing a zig rig/running zig rig. My main feed is rough liquidized bread. Although, some anglers have had success by feeding ground bait with added sugar puffs or expander pellets in the cage feeder. A running zig rig is more specialised but allows the pop-up to be fished though the layers of water to find the feeding fish!